Lee de Forest (1873-1961) was an American inventor with over 180 patents to his credit. In 1906 De Forest invented the Audion, a vacuum tube that takes relatively weak electrical signals and amplifies them. De Forest is one of the fathers of the "electronic age", as the Audion helped to usher in the widespread use of electronics. He is also credited with one of the principal inventions that brought sound to motion pictures. In 1919, De Forest filed the first patent on his sound-on-film process. Phonofilm recorded sound directly onto film as parallel lines of variable shades of gray, and later became known as a "variable density" system. He was involved in several patent lawsuits and he spent a substantial part of his income from his inventions on the legal bills. He had four marriages and 25 companies. He suffered a severe heart attack in 1958, and remained mostly bedridden until he died in 1961, aged 87.